More Like this

1. Cell dispersal by localized degradation of a chemoattractant

   https://doi.org/10.1073/pnas.2008126118  

   Karmakar, Richa ; Tyree, Timothy ; Gomer, Richard H. ; Rappel, Wouter-Jan ( February 2021 , Proceedings of the National Academy of Sciences)

   Chemotaxis, the guided motion of cells by chemical gradients, plays a crucial role in many biological processes. In the social amoebaDictyostelium discoideum, chemotaxis is critical for the formation of cell aggregates during starvation. The cells in these aggregates generate a pulse of the chemoattractant, cyclic adenosine 3’,5’-monophosphate (cAMP), every 6 min to 10 min, resulting in surrounding cells moving toward the aggregate. In addition to periodic pulses of cAMP, the cells also secrete phosphodiesterase (PDE), which degrades cAMP and prevents the accumulation of the chemoattractant. Here we show that small aggregates ofDictyosteliumcan disperse, with cells moving away from instead of toward the aggregate. This surprising behavior often exhibited oscillatory cycles of motion toward and away from the aggregate. Furthermore, the onset of outward cell motion was associated with a doubling of the cAMP signaling period. Computational modeling suggests that this dispersal arises from a competition between secreted cAMP and PDE, creating a cAMP gradient that is directed away from the aggregate, resulting in outward cell motion. The model was able to predict the effect of PDE inhibition as well as global addition of exogenous PDE, and these predictions were subsequently verified in experiments. These results suggest that localized degradation ofmore »a chemoattractant is a mechanism for morphogenesis.

   « less
2. Burkholderia bacteria use chemotaxis to find social amoeba Dictyostelium discoideum hosts

   https://doi.org/https://doi.org/10.1038/s41396-018-0147-4  

   Shu, Longfei ; Zhang, B. ; Queller, D.C. ; Strassmann, J.E. ( May 2018 , ISME)

   A key question in cooperation is how to find the right partners and maintain cooperative relationships. This is especially challenging for horizontally transferred bacterial symbionts where relationships must be repeatedly established anew. In the social amoeba Dictyostelium discoideum farming symbiosis, two species of inedible Burkholderia bacteria (Burkholderia agricolaris and Burkholderia hayleyella) initiate stable associations with naive D. discoideum hosts and cause carriage of additional bacterial species. However, it is not clear how the association between D. discoideum and its carried Burkholderia is formed and maintained. Here, we look at precisely how Burkholderia finds its hosts. We found that both species of Burkholderia clones isolated from D. discoideum, but not other tested Burkholderia species, are attracted to D. discoideum supernatant, showing that the association is not simply the result of haphazard engulfment by the amoebas. The chemotactic responses are affected by both partners. We find evidence that B. hayleyella prefers D. discoideum clones that currently or previously carried Burkholderia, while B. agricolaris does not show this preference. However, we find no evidence of Burkholderia preference for their own host clone or for other hosts of their own species. We further investigate the chemical differences of D. discoideum supernatants that might explainmore »the patterns shown above using a mass spectrometry based metabolomics approach. These results show that these bacterial symbionts are able to preferentially find and to some extent choose their unicellular partners. In addition, this study also suggests that bacteria can actively search for and target phagocytic cells, which may help us better understand how bacteria interact with immune systems.« less
3. Differential Roles of Actin Crosslinking Proteins Filamin and α-Actinin in Shear Flow-Induced Migration of Dictyostelium discoideum

   https://doi.org/10.3389/fcell.2021.743011  

   Cole, Aaron ; Buckler, Sarah ; Marcucci, Jack ; Artemenko, Yulia ( August 2021 , Frontiers in Cell and Developmental Biology)

   Shear flow-induced migration is an important physiological phenomenon experienced by multiple cell types, including leukocytes and cancer cells. However, molecular mechanisms by which cells sense and directionally migrate in response to mechanical perturbation are not well understood. Dictyostelium discoideum social amoeba, a well-established model for studying amoeboid-type migration, also exhibits directional motility when exposed to shear flow, and this behavior is preceded by rapid and transient activation of the same signal transduction network that is activated by chemoattractants. The initial response, which can also be observed following brief 2 s stimulation with shear flow, requires an intact actin cytoskeleton; however, what aspect of the cytoskeletal network is responsible for sensing and/or transmitting the signal is unclear. We investigated the role of actin crosslinkers filamin and α-actinin by analyzing initial shear flow-stimulated responses in cells with or without these proteins. Both filamin and α-actinin showed rapid and transient relocalization from the cytosol to the cortex following shear flow stimulation. Using spatiotemporal analysis of Ras GTPase activation as a readout of signal transduction network activity, we demonstrated that lack of α-actinin did not reduce, and, in fact, slightly improved the response to acute mechanical stimulation compared to cells expressing α-actinin. In contrast,more »shear flow-induced Ras activation was significantly more robust in filamin-null cells rescued with filamin compared to cells expressing empty vector. Reduced responsiveness appeared to be specific to mechanical stimuli and was not due to a change in the basal activity since response to global stimulation with a chemoattractant and random migration was comparable between cells with or without filamin. Finally, while filamin-null cells rescued with filamin efficiently migrated upstream when presented with continuous flow, cells lacking filamin were defective in directional migration. Overall, our study suggests that filamin, but not α-actinin, is involved in sensing and/or transmitting mechanical stimuli that drive directed migration; however, other components of the actin cytoskeleton likely also contribute to the initial response since filamin-null cells were still able to activate the signal transduction network. These findings could have implications for our fundamental understanding of shear flow-induced migration of leukocytes, cancer cells and other amoeboid-type cells.« less
4. Loss of the Polyketide Synthase StlB Results in Stalk Cell Overproduction in Polysphondylium violaceum

   https://doi.org/10.1093/gbe/evaa079  

   Narita, Takaaki B ; Kawabe, Yoshinori ; Kin, Koryu ; Gibbs, Richard A ; Kuspa, Adam ; Muzny, Donna M ; Richards, Stephen ; Strassmann, Joan E ; Sucgang, Richard ; Worley, Kim C ; et al ( May 2020 , Genome Biology and Evolution)

   Abstract Major phenotypic innovations in social amoeba evolution occurred at the transition between the Polysphondylia and group 4 Dictyostelia, which comprise the model organism Dictyostelium discoideum, such as the formation of a new structure, the basal disk. Basal disk differentiation and robust stalk formation require the morphogen DIF-1, synthesized by the polyketide synthase StlB, the des-methyl-DIF-1 methyltransferase DmtA, and the chlorinase ChlA, which are conserved throughout Dictyostelia. To understand how the basal disk and other innovations evolved in group 4, we sequenced and annotated the Polysphondylium violaceum (Pvio) genome, performed cell type-specific transcriptomics to identify cell-type marker genes, and developed transformation and gene knock-out procedures for Pvio. We used the novel methods to delete the Pvio stlB gene. The Pvio stlB− mutants formed misshapen curly sorogens with thick and irregular stalks. As fruiting body formation continued, the upper stalks became more regular, but structures contained 40% less spores. The stlB− sorogens overexpressed a stalk gene and underexpressed a (pre)spore gene. Normal fruiting body formation and sporulation were restored in Pvio stlB− by including DIF-1 in the supporting agar. These data indicate that, although conserved, stlB and its product(s) acquired both a novel role in the group 4 Dictyostelia and amore »role opposite to that in its sister group.« less
5. From individual behaviors to collective outcomes: fruiting body formation in Dictyostelium as a group-level phenotype

   https://doi.org/10.1093/evolut/qpac038  

   Kuzdzal-Fick, Jennie J. ; Moreno, Armando ; Broersma, Cathleen M. E. ; Cooper, Tim F. ; Ostrowski, Elizabeth A. ( December 2022 , Evolution)

   Collective phenotypes, which arise from the interactions among individuals, can be important for the evolution of higher levels of biological organization. However, how a group’s composition determines its collective phenotype remains poorly understood. When starved, cells of the social amoeba Dictyostelium discoideum cooperate to build a multicellular fruiting body, and the morphology of the fruiting body is likely advantageous to the surviving spores. We assessed how the number of strains, as well as their genetic and geographic relationships to one another, impact the group’s morphology and productivity. We find that some strains consistently enhance or detract from the productivity of their groups, regardless of the identity of the other group members. We also detect extensive pairwise and higher-order genotype interactions, which collectively have a large influence on the group phenotype. Whereas previous work in Dictyostelium has focused almost exclusively on whether spore production is equitable when strains cooperate to form multicellular fruiting bodies, our results suggest a previously unrecognized impact of chimeric co-development on the group phenotype. Our results demonstrate how interactions among members of a group influence collective phenotypes and how group phenotypes might in turn impact selection on the individual.